The oxidative polymerization of 2,6-dimethylphenol is a convenient engineering method to synthesize poly (2,6-dimethyl-1,4-phenylene ether) (PPE) as a high-performance engineering plastic in industrial fields. Recently, we reported the novel synthesis of PPE diblock copolymers based on the analysis of the polymerization mechanism. We report the preparation of PPE diblock copolymers bearing carboxylic or sulfonic acid as acid substituents. The resulting acid substituented PPE block copolymers, poly(2,6-dimethyl-1,4-phenylene ether-block-2-carboxy-6-methyl-1,4-phenylene ether) 3 and poly[2,6-dimethyl-1,4-phenylene ether-block-2-phenyl-6-(4-sulfophenyl)-1,4-phenylene ether] 5, were applied as polymer electrolyte membranes for fuel cells. 3 and 5 were soluble in polar organic solvents such as N,N-dimethylformamide, dimethylsulfoxide, and THF and gave tough membranes by casting. Sulfonated polymer 5 membrane showed high ion exchange capacity and high oxidative stability. The results suggested that the acid substituents attached onto the pendant phenyl groups were more stable than those on main chains.
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